Return of the Medfly
By: Virginia Hayes
Here they come again: The Medfly has been spotted in our area. It’s been just over 30 years since the first outbreak of the Mediterranean fruit fly (Ceratitis capitata) in Southern California. This first incidence caused widespread panic both in the agricultural industry and the urban landscape where it occurred. This little fly has the nasty habit of laying its eggs just under the skin of a variety of fruits. There, the larvae that hatch start eating the juicy insides of the fruit, causing a wound that soon supports one or more fungi to ruin it. Most fall from the tree a rotten mess to the ground, where the larvae burrow into the soil to complete their life cycle, emerging as flying adults to carry on the devastation. Since the Medfly is native to the Mediterranean region of Western Africa with a climate very similar to ours, it could adapt easily to this area. In a state with an agricultural industry measured in the tens of billions, the establishment of such a pest is not a scenario officials and growers want to contemplate.
So, state officials sprayed the area in Los Angeles from helicopters with a sticky concoction laced with Malathion (thus the panic of the populace) and eradicated the flies. They’ve been back to California periodically since then: in 1980, 1982, 1987, 1988, 1989, 1990, and 1994. Where are they coming from and how are they getting here? Extensive inspections of illegal shipments of fruit by commercial producers revealed only part of the problem. Tourists are as often to blame. Contraband fruit is subject to confiscation upon entering the state; so many people try to circumvent the inspections by mailing fruit from infected areas such as Hawaii. In one investigation, 124 larvae, 18 pupae, and two adults were found in 324 packages mailed from Honolulu to California. Today, the state maintains 130,000 traps to monitor potential outbreaks. If a single Medfly is trapped, intensive trapping in the area begins. If two are found within a three-mile radius or if one mated female, one larvae, or one pupae is found, eradication begins. One method of eradication involves releasing large numbers of sterile males, resulting in a failure of the intruders to reproduce. A more direct approach, called “male annihilation,” uses a pheromone, emitted by females to attract males, suspended in a gel containing a pesticide that kills the males when they contact or ingest it. This gel is sprayed on the trunks of trees and utility poles at a height of 8 to 12 feet. Applications are made throughout the affected area and out to a radius one-and-a-half miles in each direction from the sites where the fruit flies were found. For a map of the region, visit countyofsb.org/agcomm, click on Oriental Fruit Fly Information, then click CDFA Eradication Treatment Area Map. You will also find a schedule of treatments.
The pesticide is applied at that height to “keep it out of reach of passers-by and pets,” according to the County Agricultural Commission’s Web site. They also identify the pesticide as Dibrom. Thanks to some diligent monitoring by a few residents, it isn’t at all clear that the gel applications actually end up where they are supposed to. One witness said she saw the gel, which is sprayed from a truck, also fall on the surrounding area. While it’s a far cry from aerial spraying with Malathion in the dead of night, repeated applications of any pesticide over such a wide area, even though directed at specific targets, are cause for some concern. For residents in the area, vigilance is suggested and children and pets should be contained if you have reason to believe the gel is in reach.
Dibrom, also known as Naled and Fly Killer-D, is in the class of pesticides known as organophosphates. Purported to be moderately toxic both orally and through skin exposure, it can cause dermatitis and other skin allergic reactions on contact. Chronic exposure can lead to neurological or neuromuscular problems. Luckily, it is also very fast-acting and has a reported half-life of less than a day, rapidly degrading in the presence of sunlight to dichlorvos. Soil microorganisms break it down in the soil and plants also eliminate the bromine component to form dichlorvos. Dichlorvos remains a nerve toxin until it, too, is broken down; another half-life of 24 to 36 hours. So exposure to the sprayed gel should be avoided for a minimum of 3 days to avoid experiencing any toxic effects. Sensitive people (children and seniors) should avoid all contact.
The loss of crops and agriculture-related jobs should the Medfly become established California would be immense. Until the tide of illegal fruit arriving in the state is stemmed, limited use of pesticides will probably still be the best way to treat such outbreaks.